Reflections of a Pharmacy Practice Resident

ADS – Fluids and Sodium balance Part 1

Prior to this session, I had the opportunity to calculate a patient’s fluid balance during clinical orientation. Though I had a decent grasp on the actual calculations, I felt that I did not have a firm understanding of the rationale to why this is important.

After the ADS these are the following notes that I will be actively carrying with me throughout my rotations:

Body composition varies throughout life, in particular:

Preterm neonates are 85% TBW (basically watery sacs!)

Infants are 60% TBW; 25-30% is ECF, 30-35% is ICF

Adults are 60% TBW; 20% is ECF, 40% is ICF

If you give 1 L of:

Where does it go?

Intracellular (2/3)

Extracellular (1/3 of TBW)

Interstitial (3/4 of ECF)

Intravascular (1/4 of ECF)

D5W

666 mL

250 mL

84 mL

0.9 NaCl (NS)

0

750 mL

250 mL

D5NS

0

750 mL

250 mL

½ NS

333 mL

500 mL

168 mL

D5-½NS

333 mL

500 mL

168 mL

3% NaCl

0

~750 mL *some H2O moves here from ICF

~ 250 mL *some H2O moves here from ICF

Albumin, blood, pentaspan

0

0

1000 mL

How to calculate maintenance fluid requirements: 4/2/1 method

Holliday-Segar Method (/day)

Estimate (/hr)

First 10 kg

100 ml/kg

4ml/kg

Second 10kg

50 ml/kg

2 ml/kg

Every kg thereafter

20 ml/kg

1ml/kg

Maintenance Needs:

Sodium ~ 3mmol/kg/day (this is likely to be an underestimate, as sick kids need more, and by only giving 3 mmol/kg/day you may cause iatrogenic hyponatremia)

Potassium: 2 mmol/kg/day

Orders would look like this: D5-1/2NS + 30 mmol/L KCl IV at 63 ml/hr

Deficit Needs: to “fix” a deficit – these are fluids lost prior to medical care and should be assessed by degree of dehydration, for every 1 kg of weight loss = 1 liter of fluid loss